Exemplary embodiments of the present invention relate to a metering arrangement with a metering device for the feeding of a reducing agent solution for the exhaust gas after-treatment in an exhaust gas system. The metering device is connected with a supply container for the reducing agent solution via at least one pipeline. At least one heating device is provided for the heating of at least one component of the metering arrangement. Furthermore, exemplary embodiments of the present invention involve a method for the operation of such a metering arrangement.
A known prior art metering system includes a metering device that feeds an aqueous urea solution into an exhaust system. This serves as a reducing agent solution in the exhaust system for the provision of ammonia, which then, in a selective catalytic reduction reaction with the oxides of nitrogen present in the exhaust gas forms nitrogen and water. This reduction reaction takes place in a so-called SCR-catalytic converter (SCR=selective catalytic reduction). The freezing point of a commercial aqueous urea solution lies below that of water, and it can freeze at very low outside temperatures of less than −11° C. From the prior art it is known, that a pump in which there is a frozen urea solution can be thawed out by means of a heating device and the thawed out aqueous solution then delivered by the pump from a supply container to a metering device.
Previously, damage to the components of such a generic type of metering arrangement has been observed as a consequence of the freezing up of the reducing agent solution.
Exemplary embodiments of the present invention are directed to a metering arrangement and a method for the operation of such a metering arrangement, which offer particularly good protection from damage caused by the frozen reducing agent solution.
The metering arrangement according to the invention, which is particularly intended for a vehicle, comprises a metering device, by means of which a reducing agent solution for the exhaust gas after treatment can be fed into an exhaust system. The metering device is connected via at least one pipeline with a supply container for the reducing agent solution. At least one heating device heats at least one component of the metering arrangement. Here at least a first component of the metering arrangement is assigned a first heating device, which is arranged operable separately from a second heating device for the heating of at least a second component of the metering arrangement in such a way, that a point in time of the freezing and/or a point in time of the thawing of the first component or of a section of the first component can be established in relation to a point in time of the freezing and/or a point in time of the thawing of the second component and/or of a section of the second component. In this way, through targeted operation of the respective heating device it can be ensured that first the at least first component and then the least second component of the metering arrangement are heated and thus the frozen reducing agent solution present in the respective components is thawed out. Furthermore the sequence and the point in time of the freezing of the components or of a section of a respective component of the metering arrangement on a freezing of the reducing agent solution in the metering arrangement can be fixed and thereby damage due to freezing avoided.
This is based on the knowledge that a customary aqueous reducing agent is at its largest specific volume when the solution is frozen and the temperature of the frozen solution corresponds to that of the freezing point of the solution. However, a further cooling of the reducing agent solution is accompanied by a reduction in volume. Correspondingly, the volume of the frozen solution increases when is heated from a temperature below the freezing point up to the freezing point. Therefore, if the frozen reducing agent solution in a first component is present and this is then thawed out, whilst neighboring components still contain the frozen solution, then the increase in volume of the reducing agent solution within the first component leads to a strong force, which can lead to damage to this component.
In accordance with exemplary embodiments of the present invention, an offset in time of the operation of the heating devices is provided, in which a sequence of the thawing of the reducing agent solution exists in the components of the metering arrangement, which takes into account the sensitivity of the individual components with respect to the force exerted on the individual components due to the increase in volume of the reducing agent solution. Thus, the most sensitive component can be thawed last, so that space is created to be taken up by this component of the reducing agent solution in the increase in volume of the reducing agent solution accompanying the approach to the freezing point from a temperature below the freezing point. This can prevent damage due to the frozen reducing agent solution.
If a control device for the operation of at least one of the heating devices is formed as an electronic control unit, this can be used very simply for the activation or deactivation of electrical heating devices. If at least one of the heating devices is formed as a heat exchanger, then by means of the control of valves and similar shut off devices it can be ensured that certain heating devices give out heat and others do not. Also, an electronic control unit of and in conjunction with the metering arrangement can control at least one heating device in determining whether at least one heat exchanger is to used for the heating of the assigned component of the metering arrangement. Also the triggering of an electrical heating device can take place at the same time or with a time delay for the heating by means of a heat exchanger.
Analogously to thawing, the heating devices can be operated with a time offset, in order to achieve a sequence of the freezing of the components of the metering arrangement. The basis for this is the knowledge that the freezing of the reducing agent solution, commencing from the liquid condition of the solution, is likewise accompanied by an increase in volume. If at a position of the metering device additional volume generated through freezing cannot be displaced, for example because the surrounding areas are already frozen, then likewise damage to the metering arrangement can occur. It is therefore preferably provided that through a time control of heatings a freezing, especially of a mechanically sensitive area of the metering arrangement, or of a component of the metering arrangement, is facilitated before a freezing of neighboring areas is enabled. Those existing heating devices, which are assigned to predetermined, in particular to mechanically sensitive components of the metering arrangement, can be deactivated in a targeted fashion, or simply not operated.
It can be provided, that a component, whose parts would be particularly heavily loaded through the freezing of the reducing agent solution if it would freeze last, is simply not heated. If a first heating device is not operated, then a cooling down of at least one of the components of the metering arrangement assigned to the first heating device to below the freezing point of the reducing agent solution is permitted. Consequently the reducing agent solution in this first, sensitive component, freezes first and before other, heated components.
Furthermore a second heating device can be operated in such a way, that a second components of the metering arrangement assigned to the second heating device is held at a temperature above the freezing point. While the second heating device prevents a freezing of the reducing agent solution in the at least one second component, the freezing of the at least one first, sensitive component or of an area of the component is permitted. The freezing of the reducing agent solution in at least a second component is hereby uncritical in respect of the accompanying increase in volume associated with the freezing. Thus, the reducing agent solution freezes last in the second, insensitive component or after the first component respectively.
Since the heating devices assigned to the respective components can be operated separately from each other, a time-based sequence of the freezing of the components of the metering arrangement can thus be provided, when the heating device assigned to the respective component is correspondingly operated with an offset in time to another heating device of the metering arrangement. Thus, sensitive components can be protected by defining the sequence of the initiation of the heating devices.
Thus, the sensitive components of the metering arrangement can be devised comparatively cost-effectively, since expensive precautions can be avoided, which facilitate the compensation of an increase in volume of the reducing agent solution found in the components. Also, individual parts of a sensitive component can be designed such that they merely cope with the rise in pressure accompanying a minimal increase in volume of the reducing agent solution, which is brought about when the components last or freeze first. Thus, by this means a particularly good protection can be achieved against damage due to the frozen reducing agent solution, and at the same time a metering arrangement can be created with favorably-priced components.
In an advantageous embodiment of the invention in a thawing operation, at least a section of the at least one second component of the metering arrangement is brought from a temperature below the freezing point to the temperature of the freezing point of the reducing agent solution at a point in time before this is achieved by the at least one first component. If, for example, the second component is the supply container and the first component is the metering device, then in the thawing mode by appropriate time-wise offset operation of the heating devices it can be arranged that first the frozen reducing agent solution in the supply container is thawed out and then the frozen reducing agent solution in the metering device is thawed out.
Furthermore, the sensitive components of the metering arrangement can be thawed out last and the less sensitive components of the metering arrangement can be thawed first. Thus, the less sensitive components already containing the thawed out reducing agent solution provide a reception volume, in which liquid reducing agent solution formed on the thawing of the later heated components can be absorbed. In addition, the increased volume of the frozen reducing agent solution that forms on the heating up of the frozen reducing agent solution from the temperature below the freezing point to the temperature of the freezing point, can ingress into the reception volume.
In a further advantageous embodiment of the invention the at least one first component comprises the metering device of the metering arrangement. This component is thus relatively complex and sensitive. A thawing of the metering device or certain volume areas of the metering device before a thawing of neighboring areas of the metering device or of neighboring components of the metering arrangement or of components of the metering arrangement that are connected together can therefore cause particularly undesirable damage. The same applies for a freezing of the metering device or certain volume areas of the metering device after a freezing of neighboring areas of the metering device or of neighboring components of the metering arrangement or of components of the metering arrangement that are connected together. If, however, in the area of the metering device or in certain volume areas of the metering device a freezing of the reducing agent solution is allowed to occur before a freezing of neighboring volume areas of the metering device or before a freezing of components connected to the metering device, possibly in that an assigned first heating device is operated independently or with a time offset with respect to a second heating device, then the frozen reducing agent solution can find its way into surrounding, as yet unfrozen areas, of the metering arrangement, and damage to the sensitive metering device is avoidable. Also the volume increase of the reducing agent solution approaching the freezing point from a lower temperature can thus be compensated.
Alternatively or additionally, the at least one first component of the metering arrangement comprises a pump device for the pressurization of the metering device with the reducing agent solution. With such a pump device a particularly marked increase in the internal pressure can occur due to an early approach to the freezing point, due to a thawing before that of other components, leading to damage, which should be avoided. The same applies to a late freezing of the pump device. In other words the pump device is also a comparatively sensitive component and thus requires protection in special measure, preferably taking account of the sequence of the components freezing one after the other, and preferably likewise being given attention with a priority similar to that of the metering device.
On thawing it is, on the other hand, favorable if the pump device is only warmed up from a temperature below that of the freezing point of the reducing agent solution to the freezing point, when components of the metering arrangement bounding the pump device have already created space for the extra volume itself, due to thawing of the solution.
It has further been shown to be advantageous if the at least one second component of the metering arrangement comprises an entry pipe leading to the metering device and/or a return pipe leading from the metering device to the supply container. If these pipes contain liquid reducing agent solution due to heating of the latter, then the increase in volume of the reducing agent solution in the area of the metering device and/or in the area of the pump device, heated or cooled to the freezing point is not hindered by frozen connecting pipes.
In a further advantageous embodiment of the invention, the at least one second component of the metering arrangement comprises the supply container. If this supply container on freezing is held until last at a temperature, which is above the freezing point of the reducing agent solution, the increasing additional volume to be received due to the freezing of the remaining components of the metering arrangement can particularly simply arrive in the supply container. On the other hand, when thawing the metering arrangement the supply container can be heated up particularly favorably before the remaining components of the metering arrangement. Then the supply container can simply absorb the additional volume of the reducing agent solution, which then on subsequent heating up the remaining components of the metering arrangement builds from a temperature below the freezing point up to the freezing point.
Preferably the heating devices can also be operated in such a way, that a cooling off of the inlet pipe and/or of the return pipe to a temperature below the freezing point of the reducing agent solution is permissible before the cooling of the supply container to this temperature. This takes account of the fact that a freezing of the reducing agent solution in the inlet pipe or in the return pipe is uncritical if the pipe is blocked on one side by frozen reducing agent solution. These pipes of the metering arrangement can be simply and economically constructed from a material, which is adequately elastic to cope with the increase in volume of the reducing agent solution.
This also applies when, additionally or alternatively, the heating devices can be operated in such a way that a heating up of the inlet pipe and/or the return pipe to the freezing point takes place after the heating up of the supply container to this temperature. If frozen reducing agent solution expanding when warmed up to the freezing point presses from the supply container into the pipes, these pipes may yield if they are formed from an elastic material. For example, synthetic elastomer material can be used as a material for the pipes, in particular such as Ethylene-Propylene-Diene rubber or Ethylene-Propylene-DieneMonomer (EPDM).
A further advantage can be achieved if the metering arrangement incorporates a heating device for the heating of a section of pipe leading from the supply container to a pump device and a further heating device for the heating of another section of pipe leading from the pump device to the metering device. Thus, a detailed sequence of the freezing or the thawing of the sections of pipe can be provided, in that the timing of the operation of the heating devices is appropriately sequenced.
Finally, it has also been shown to be advantageous if a control device designed for controlling at least one of the heating devices is coupled with a temperature sensor for the acquisition of an outside temperature. In this way, the necessary heating power can be particularly well adjusted to the thawing process. Also, during the initiation of the freezing of the components in a desired sequence, the heating power and/or the sequence or the duration of operation of a heating operation can be appropriately effectively and efficiently adjusted when the outside temperature is taken into account in the control device. In particular, subsequent to a switching off of an internal combustion engine of the vehicle, a first heating device of a component of the metering arrangement can be operated in a post-heating operation. Particularly preferred is the provision of a post heating operation, when it is established that the outside temperature lies below an adjustable prescribed threshold temperature of, for example, minus 11° C.
Such a post heating operation of an individual heating device or of a part of available heating devices of the metering arrangement can comprise an arrangement in which the corresponding heating device(s) remain(s) active after shut-down of the internal combustion engine for a prescribed period of time or is/are activated for a prescribed period of time, while other heating devices of the metering arrangement remain deactivated or are deactivated. In the post heating operation it can also be provided that one or more selected heating devices of the metering arrangement can be switched on after a first prescribed period of time directly after the shut-down of the internal combustion engine for an inactive period of time, for a prescribed second period of time. By this means a freezing of an assigned area or of assigned areas of the metering arrangement can be effectively delayed or prevented.
In the post heating operation a continual, unbroken heating or a timed period of heating can be provided with a predetermined timing ratio, preferably dependent on the outside temperature and with alternating on and off phases. In this case the time span of the active switching can relate to the duration of the timed operation. By means of a timed operation, with On phases, for example in the minutes range, and Off phases, likewise in the minutes range, a freezing of such a type of heated area is prevented with a reduced heating capacity. The first and the second time periods are thereby preferably established as a function of the outside temperature as determined by the temperature sensor. Also, the timing ratio with a time-based cycled heating operation can be established as a function of the outside temperature. This can take place, for example, through appropriate preliminary investigation. The post heating operation is preferably terminated when areas neighboring the heated area are frozen and a volume expansion is no longer expected from these areas.
In the method for the operation of a metering arrangement according to the invention, which comprises a metering device for the introduction of a reducing agent solution for the exhaust gas after treatment in an exhaust system, whereby the metering device is connected with a supply container for the reducing agent solution via at least one pipe, at least one component of the metering arrangement is heated by means of at least one heating device. At least one first component of the metering arrangement is heated by means of an assigned first heating device, which is operated separately from at least one second heating device assigned to a second component of the metering arrangement.
The method, by which through the separate heating of different components of the metering arrangement and/or different areas of a component of the metering arrangement a freezing or thawing sequence of components or a freezing or thawing point in time of a component or of an area of a component of the metering arrangement is determined, enables a particularly good protection to be provided for sensitive components of the metering arrangement from damage caused by the frozen reducing agent solution.
The advantages and preferred embodiments described for the metering arrangement according to the invention are also applicable to the method according to the invention and vice-versa.
The features and combinations of features named in the description above, as well as those named in the following description of the figures and/or shown only on the figures are not solely applicable to the respective given combinations, but also in other combinations or on their own, without relinquishing the framework of the invention.
Further advantages, features and details of the invention result from the claims, the following description of preferred embodiments and also on the basis of the drawing.